1. Field of the Invention
The present invention relates to an exposure method, an exposure apparatus and a semiconductor device manufactured by using the exposure apparatus. More specifically, the present invention relates to an exposure apparatus capable of reducing stage matching error, which is a registration error generated when a plurality of exposure apparatuses are used, and to a semiconductor device manufactured by using the exposure method.
2. Description of the Background Art
Conventionally, an apparatus called a stepper has been known as an exposure apparatus used for manufacturing a semiconductor device. In the stepper, a semiconductor wafer is moved stepwise in X-Y direction below a projection lens, while an exposure pattern image formed on a reticle is reduced by the projection lens and the image is exposed successively on each shot area of one semiconductor wafer.
Various methods for improving registration accuracy have been employed for the stepper. An alignment method disclosed in Japanese Patent Laying-Open No. 61-44429, for example, has been known as a method of improving registration accuracy.
The aforementioned alignment method disclosed in Japanese Patent Laying-Open No. 61-44429 will be described with reference to FIG. 9. FIG. 9 is a schematic flow chart of an exposure sequence using EGA (Enhanced Global Alignment) method described in Japanese Patent Laying-Open No. 61-44429.
Referring to FIG. 9, a semiconductor wafer is subjected to pre-alignment, using an orientation flat of the semiconductor wafer (step D10).
Thereafter, using a WGA (Wafer Global Alignment) mark formed in each shot area, the semiconductor wafer is rotated for correction (step D11).
Thereafter, a stage on which the semiconductor wafer is mounted is moved in accordance with a design value of chip arrangement, and for a plurality of shot areas selected in advance for error detection, an LSA alignment mark position of print pattern is detected by an LSA (Laser Step Alignment) optical system (actually measured value). At the same time, the position of the wafer stage is detected by a laser interferometer (design value).
Based on the detected actual measured value and the design value, registration error between the print pattern on the semiconductor wafer and the reticle pattern image is detected (step D12).
Thereafter, based on the design value and the actually measured value, error parameter is determined by least square method. More specifically, registration error in each shot area and deviation from a position coordinate (coordinate of the print pattern) on the wafer stage are found. An average value of the deviation is calculated as a correction value (error parameter) (step D13).
Using the error parameter and the design value, a chip arrangement map is formed in which rotation error, perpendicularity, base line error and scaling error in each shot area are corrected (step D14).
Thereafter, in accordance with the chip arrangement map, the wafer stage is positioned by step and repeat method (step Dl5). Thereafter, each shot area is exposed (step D16).
The exposure method using the EGA method described above utilizes four correction values (error parameters), that is, base line correction, rotation correction, perpendicularity correction and scaling correction. An exposure pattern is obtained with registration accuracy improved by using these four correction values.
Now, in the exposure method based on the EGA method using the aforementioned four correction values, the errors to be corrected are linear errors experienced when the semiconductor wafer is placed on the wafer stage. When first and second exposure steps are performed by one exposure apparatus, non-linear errors inherent to the exposure apparatus including an error derived from distortion of an interference mirror and peculiar tendency of travel of the stage do not cause any problem, as such errors are cancelled.
When the exposure steps are performed by using a plurality of exposure apparatuses, non-linear errors of the exposure apparatuses differ apparatus by apparatus. Accordingly, the non-linear errors cannot be cancelled among the exposure apparatuses, resulting in lower registration accuracy.